During rotary drilling, a drill bit is rotated from the surface of a well by rotating a drill string. It is often desirable to control the direction in which the drilling proceeds through use of a downhole steerable drilling apparatus. Steerable drilling apparatuses include hydraulic devices that apply a lateral bias to a drill string, bent or bendable housing members for drilling at angles, and rotary devices that use a rotatable member, actuators, and/or retractable members to control the direction of the drill string.
Conventional downhole rotary directional drilling assemblies use gravity and compression to force an under gauge stabilizer to the bottom side of a hole, with a drill collar acting as a lever, and a near bit stabilizer acting as a fulcrum. This lever-like motion pushes the drill bit upward, causing the drill bit to drill on the top of a hole, thereby increasing the angle of the hole. The angle of the drilling can be modified through changes in the length of the drill collar, the diameter of the stabilizers, or modifying one or more drilling parameters.
Conventional rotary directional drilling assemblies can steer a drill bit only within a single plane, and not along the azimuth.
A need exists for a rotary directional drilling apparatus that can allow an operator to steer a drill string in any direction, controlling directional changes both in hole angle and along the azimuth.
A need also exists for a rotary directional drilling apparatus that can utilize fixed steering elements without use of actuators, rather than conventional retractable and movable biasing and thrusting members.
A further need exists for a rotary directional drilling apparatus able to selectively adjust the orientation of a drill bit through control of the flow of drilling fluid or mud through the mud motor.
The present embodiments meet these needs.